Nuclear medical imaging such as single-photon emission computed tomography (SPECT) and positron emission computed tomography (PET) have become important tools in pre-clinical and clinical imaging applications. Most commercially available cameras used in SPECT and PET still rely on photomultiplier tubes (PMTs) to detect the scintillation light from the conversion of the gamma rays in the scintillator. The success of PMTs in nuclear medicine is largely due to the fact that they are very high-gain, fast-response, and low-noise photodetectors. However, PMTs have a number of limitations: they are relatively bulky, they are relatively expensive, they are fragile vacuum tube devices, they have relatively low optical quantum efficiency, and they cannot operate under high magnetic fields. As a result, the use of PMTs limits the development of advanced detector concepts in nuclear medical imaging such as high-resolution scanners and multi-modality imaging. For example, there is an increasing interest in multimodality imaging, which combines the power of functional imaging of nuclear medicine with the excellent structural imaging of X-ray computed tomography (CT) or magnetic resonance imaging (MRI). Since PMTs cannot operate under high magnetic fields, alternative photodetectors is required. An attractive alternative to PMTs that has been under active investigations by many groups for applications in radionuclide imaging is solid-state photodetectors. The goal of this is project to develop a solid-state photodetector with better performance than currently available. The novel and innovative approach of our proposed device is to translate the amplification structure that has been successfully applied in gaseous detectors to semiconductors devices through advanced semiconductor and microfabrication technology. The advantages of this new approach are solid-state photodetectors with: (1) high particle detection efficiency (PDE);(2) the region of avalanche controlled by the geometric parameters of the structure rather than by the dopant concentrations and dopant profile of the semiconductor;(3) low thermally generated noise;(4) relatively low capacitance;and (5) the gain controlled by the geometric parameters of the structure such as channel length and area as well as the applied voltage, which will allow operation in proportional mode or Geiger mode. This project has the promise of photodetectors with the gain and bandwidth of PMTs and the quantum efficiency, cost, and compactness of silicon photodiodes, which would have a tremendous benefit to the development of advanced detectors in nuclear medical imaging. PUBLIC HEALTH RELEVANCE: The development of compact, low-cost solid-state photodetectors with high signal-to-noise ratio, high sensitivity, and high-gain will have a large impact on national health care through the development of advanced detector concepts in radionuclide medical imaging such as high-resolution scanners and multi-modality imaging.